1. A stock STi is faster than your car based on the time in your sig (TRACK: 1/4 MILE 13.66 102.7 MPH).
2. I know plenty of regular people that can run low 13s in their stock M5. You don't need to be a professional driver to do it.
3. A stock M5 has about 15% drivetrain loss so that puts the power at 394 HP * 85% = 335 HP